1. Technical Field
The present invention relates generally to collision countermeasure systems, and more particularly to a method and apparatus for determining occupant classification within an automotive vehicle.
2. Background of the Invention
Collision countermeasure systems are becoming more widely used in automotive vehicles. Countermeasure systems exist in various passive and active forms. Active countermeasure systems are used to aid in prevention of a collision, while passive countermeasure systems are used to aid in the prevention of injury to vehicle occupants in the event of a collision. Examples of passive countermeasures are seat belt pretensioners, air bags, and load limiting seat belts.
Some countermeasure systems consider the weight and/or size of one or more vehicle occupants in determining whether to implement and to what extent to implement an active or passive countermeasure. Gauging or measuring of an occupants weight and/or size will be referred to herein as occupant classification. For example, in the case of an occupant restraint air bag, occupant classification is used as one input or factor in making a decision as to whether to deploy an air bag and/or the appropriate air bag deployment rate. Generally, the larger/heavier the occupant, the higher the rate at which the air bag is deployed.
Known occupant classification systems have several disadvantages associated with them. Some occupant classifications systems use a sealed bladder-type device incorporating a pressure sensor. The bladder is mounted on a seat pan so that the seat occupant sits on top of the bladder and compresses it. The larger the force on the bladder the higher the pressure created in the bladder, which is directly related to the mass of the occupant. An approximately linear relationship is created between the sensed pressure and the weight on the seat system. Under static conditions, the use of a bladder and pressure sensor alone can be fairly accurate, but dynamically the amplitude of the pressure signal generated by the pressure sensor is continuously changing for the same occupant, therefore resulting in false or erroneous occupant classifications.
A seat system typically includes a seat pad disposed on the seat pan, the pad comprising foam or a similar cushioning material. The properties (density, resiliency, etc.) of the foam affect the slope, or gain of the pressure versus weight curve. The properties of the foam change over time as the foam ages and is repeatedly compressed and released during use. Other seat system characteristics also may change over time, further altering the offset and/or gain of the curve. The changing characteristics of the seat system components may cause errors, leading to an increase in the likelihood of false occupant classifications. The countermeasure system may, for example, determine that an occupant is present in the seat system when in actuality an occupant is not present.
To solve the problem of continuously varying seat system characteristics, the occupant classification system may need to be continuously recalibrated or eventually replaced. Recalibration and replacement of the occupant classification system can be costly and time consuming, and may even require replacement of the full seat system and calibration of the new replacement seat system, further increasing costs.
Known weight sensing occupant classification systems may also be prone to false classifications due to seat belt cinching. When a seat belt is buckled around a child safety seat, for example, and tightened, the force of the belt on the child seat is transferred into a downward force on the seat pan, thus artificially increasing the sensed weight. In order to eliminate this problem, seat belt tension sensors are used to measure the tensile force in the belt, and the sensed weight is corrected to compensate for the extra downward loading caused by the belt tension. The addition of seat belt tension sensors provides additional costs in production of the seat system as well as the occupant classification system.
Typically, a particular occupant classification system is calibrated and used with a single type of seat having specific characteristics. Each seat system has different characteristics due to the seat foam, seat cover, seat frame, seat tracks, and other components between the occupant and the occupant classification sensors, and even the vehicle structure to which the seat is mounted. In other words, each occupant classification system is seat specific. Moreover, during a collision event or simply in replacement of a seat system the full occupant classification system may need to be replaced and recalibrated for a new seat system.
Some occupant classification systems use load cells mounted rigidly between the seat frame and the vehicle seat floor mounts to measure occupant weight. The use of load cells reduces replacement costs but does not resolve the false classifications due to dynamic loading or unforeseen use events. When the seat belts are mounted directly to the seat system above the load cells, seat belt tension sensors may not be necessary to correct for seat belt cinching. But if the seat belts are mounted to some portion of the vehicle separate from the seat system (such as to a B-pillar) seat belt tension sensors are still required.
More sophisticated occupant sensing systems are known to use accelerometers to measure vertical acceleration of the seat pan so as to determine that the seat pan is in dynamic motion, and to adjust for this motion and thereby minimize offset errors. In using the accelerometers, the pressure versus weight curve is adjusted by shifting the curve up or down to remove a false zero-offset. Also, as with the load cells, seat belt tension sensors are still required to overcome the problem of seat belt cinching.
Another existing disadvantage with current occupant classification systems, that may become more evident in the future, is that of production variation in a single seat system. Currently, to resolve production variation each occupant classification system is individually calibrated or zeroed. But in order to satisfy upcoming and more stringent government regulations the operating variation between identical occupant classification systems for a particular seat system need to be minimized, to satisfy tighter tolerances in classifying an occupant.
It is desirable to provide an improved occupant classification system for use in a collision countermeasure system of an automotive vehicle that eliminates or minimizes false occupant classifications and is more accurate in determining classification.
The foregoing and other advantages are provided by a method and apparatus for classifying an occupant within an automotive vehicle. An occupant classification system for an automotive vehicle is provided. The system includes a weight-sensing device that generates a weight signal and an accelerometer that generates an acceleration signal. The weight-sensing device and the accelerometer are coupled to a seat system. A controller is electrically coupled to the weight-sensing device and the accelerometer. The controller determines occupant classification in response to the weight signal and the acceleration signal by monitoring a frequency domain representation of the weight signal divided by the acceleration signal. A method for performing the same is also provided.
One of several advantages of the present invention is that it provides a system that accurately determines occupant classification during dynamic loading of a seat system.
Another advantage of the present invention is that it determines occupant classification independent of seat belt cinching.
Additionally, the present invention determines occupant classification independent of seat system characteristics.
Therefore, the present invention maybe used in various seat systems without recalibration. Also the present invention may operate in the various seat systems without false occupant classification due to usage and age of the seat system. Furthermore, the present invention may be removed from an old seat system and reused in a new seat system saving costs in system replacement and calibration.
Another advantage of the present invention is that it provides increased vehicle intelligence as in assessing occupant classification and determining whether to perform a countermeasure and at what rate to perform that countermeasure.
The present invention itself, together with attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying figures.